For ganache

3 tablespoons heavy whipping cream

1 teaspoon light corn syrup

1 1/2 ounces bittersweet chocolate, chopped

1 tablespoon hot water

Maldon sea salt crystals or other coarse sea salt

To prepare caramel filling: Place the cream and butter in a small, microwave-safe bowl; microwave on high power until simmering, about 15 seconds. Place the sugar, water and corn syrup in a small, heavy saucepan; bring to a boil, stirring until the sugar melts. Boil, uncovered, until the mixture is caramel-colored. Remove from the heat and immediately, but slowly, whisk in the hot cream mixture with a long-handled whisk. (The mixture will splatter.) Whisk in the vanilla. Pour into the pastry shells. Divide nuts and sprinkle evenly over the caramel. Refrigerate until cool.

To prepare the ganache: Place the cream and corn syrup in a small microwave-safe bowl; microwave on high power until simmering, about 25 seconds. Stir in the chocolate until smooth. Stir in the hot water until blended. Pour over caramel in tarts, dividing evenly. Let stand until chocolate is set, about 1 hour. Sprinkle lightly with sea salt and serve.